The invention relates to a passive radiator comprising a frame and a radiator body which is connected to said frame and which is movable with respect to said frame along a translation axis.
Such a radiator is known from U.S. Pat. No. 3,669,215 and is designed for use in a bass reflex loudspeaker system. The known passive radiator comprises a basket-shaped frame and a conical body which is suspended from the frame. The suspension used consists of a deformable suspension ring which extends between a greatest circumferential rim of the conical body and the frame. A plate is fastened to the smallest circumferential rim of the conical body and is also fastened to a back part of the frame via three elastic wire elements. This suspension allows of limited axial displacements of the conical body with respect to the frame only, so that major volume displacements, i.e. displacements of major quantities of air, are only possible if the conical body has large lateral dimensions.
It is an object of the invention to improve the passive radiator mentioned in the opening paragraph such that displacements of comparatively large air volumes are possible while the radiator has limited transverse dimensions.
This object is achieved with the passive radiator according to the invention which is characterized in that the radiator body comprises a central mass element and at least one mass element concentrically positioned with respect to the central mass element, while connection units are present for the movable interconnection of every two mutually adjoining mass elements and for the movable fastening of one of the mass elements to the frame, each of said connection units comprising at least a resilient annular connection element, the central mass element with its adjoining connection unit forming a mass spring system, as does each conically positioned mass element with its adjoining connection elements, while all mass spring systems present and thus defined have at least substantially the same resonance frequency.
The use of two or more mass elements which are interconnected by resilient connection elements leads to a construction with a multiple suspension in which each mass element present contributes to the total air displacement during use. A mass element performs individual movements with respect to an adjoining mass element along the translation axis of the radiator body during operation, which results in displacements with respect to the frame which are cumulations of individual movements. Comparatively large displacements of mass elements can be realized in this manner, so that considerable volume displacements can be achieved with a comparatively small radiator body. To counteract parasitic resonances during use, it was found to be necessary for the mass spring systems present in the passive radiator according to the invention as defined above to have the same or practically the same resonance frequency. If this requirement is not complied with, movements of individual mass elements may get out of phase, so that serious sound distortions and/or attenuations may arise during use. Damping means may be used, if so desired, for counteracting irregularities in movements of individual mass elements.
It is noted that WO-A 97/46047 (PHN 15.840) discloses a passive radiator which comprises a frame, a mass element, and a sub-frame extending between the mass element and the frame, while the mass element is movably fastened to the sub-frame by means of a first resilient suspension ring and the sub-frame is movably fastened to the frame by means of a second resilient suspension ring. The maximum stroke of the mass element is defined by the sum of the maximum strokes of each of said suspension rings. Although a reasonably large volume displacement is possible with this known construction, it was found that a greater maximum stroke is desirable at higher powers so as to prevent harmonic distortion in the low frequency range.
An embodiment of the passive radiator according to the invention is characterized in that the connection units allow mainly of movements of the mass elements along the translation axis of the radiator body and counteract other movements. It is prevented in this embodiment that the mass elements perform disadvantageous tilting movements with respect to one another during operation, which tilting movements could lead to distortions in the sound reproduction. The annular connection elements used may be made from resilient materials which are known per se such as polyurethane or rubber and preferably each have a folded or wave structure. Shape and dimensions of the connection elements lie within comparatively narrow limits which are defined inter alia by the required resistance to pressure variations which occur during operation and the capacity of deforming in a flexible manner, i.e. without disadvantageous effects such as kinking or abutting, during the movement of the mass elements. A connection element which is too slack and/or not flexibly deformable gives rise to undesirable distortions, especially distortions of the second and higher order, in the sound reproduction and accordingly to unpleasant additional noises. An increase in the size of the suspension ring of the radiator known from U.S. Pat. No. 3,664,215 or an increase in the size of the suspension rings of the radiator known from WO-A 97/46047 will not lead to satisfactory results for this reason. A greater volume displacement achieved in that manner will in fact be accompanied by an impaired sound reproduction quality.
An embodiment of the radiator according to the invention is characterized in that at least a number of the connection elements comprise a further resilient annular connection element, which further connection element and the connection element mentioned earlier of such a connection unit are at a distance from one another, measured along the translation axis of the radiator body. This embodiment is particularly suitable if, instead of a plane or thin radiator body, a radiator body with a considerable axial dimension is used, i.e. a dimension in a direction parallel to the translation axis of the radiator body. The specific configuration of connection elements used in the present embodiment safeguards well-defined displacements of the mass elements of the radiator body, so that swinging movements as a result of pressure variations and/or parasitic resonances can be avoided.
An embodiment of the radiator according to the invention is characterized in that the number of mass elements is three or four. Although a different number of mass elements is possible, it was found that a design with three or four mass elements can be well realized in practice for achieving a displacement of a comparatively large air volume.
An embodiment of the radiator according to the invention is characterized in that the connection elements are mutually identical. This embodiment is preferable if the object is to give each mass element the same maximum axial stroke with respect to its adjoining mass element or adjoining mass elements. In a practical embodiment, the connection elements may be, for example, omega-shaped. Any further connection elements, if present, are preferably provided in mirrored positions with respect to the other connection elements so as to prevent asymmetry in the displacements and amplitudes of the mass elements.
An embodiment of the radiator according to the invention is characterized in that at least a number of the connection elements are of mutually different sizes, said size increasing in a direction away from the central mass element. It is achieved by this measure that an annular mass element is capable of performing a relatively greater maximum displacement than a central mass element which is present, i.e. compared with its respective adjoining central or more centrally positioned mass element each time. An advantage of this configuration is that the strokes of the connection elements are optimally utilized without undesirable deformations of the connection elements occurring.
An embodiment of the passive radiator according to the invention is characterized in that the radiator body and the connection units are together constructed as one integral unit. The mass elements and the connection elements in such a unit are preferably manufactured from one material, such as rubber. The integral unit may be constructed as a skin, in particular a thin skin, which is fastened with its circumferential edge to the frame. The number of mass elements in this embodiment may be much larger than the number of three or four mentioned elsewhere in this description.
The invention further relates to a loudspeaker system comprising a housing or cabinet which accommodates an electrodynamic loudspeaker and a passive radiator. The loudspeaker may be of any type which is known per se. The passive radiator present in the loudspeaker system according to the invention is constructed as defined in one of the claims 1 to 7. The connection units and the passive radiator in the system according to the invention allow of mutual displacements of the mass elements defined by pressure variations in the housing, which displacements result in comparatively large air displacements, so that a comparatively large sound pressure can be achieved.
Preferably, the loudspeaker system according to the invention is constructed as defined in claim 9. It is safeguarded in such a system that the various connection units allow of strokes under the influence of pressure variations in the housing which are fully attuned to the total moving mass of the radiator and the tuning frequency, the so-called Helmholz resonance, of the system.
The invention further relates to a device for providing audible, and possibly also visible information, which device according to the invention is provided with the loudspeaker system according to the invention.
It is noted about the claims that various combinations of characteristics as defined in the dependent claims are possible.